Process of and apparatus for renovating coated metal sheets



June 5, 1923.

c. F. H. BOHNHARDT PROCESS OF AND APPARATUS FOR RENOVATING COATED METALSHEETS AJune 5, 1923. 1

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1,457,688v c. F. H. BOHNHARDT PROCESS OF' AND APPARATUS FOR RENOVATINGCOATED METAL SHEETS Filed MaICh 8, 1919 3 Sheets-Sheet 5 Patented June5, 1923.

UED STATES CHARLES F. H. BOHNHARDT, OF BALTIMORE, MARYLAND,

ASSIGNOR TOv THE CROWN CORK AND SEAL COMPANY OF BALTIMORE CITY, OFBALTIMORE, MARYLAND, A

CORPORATION OF MARYLAND.

PROCESS OF AND APPARATUS FOR RENOVATING COATED METAL SHEETS.

Application mea march s, 1919. seriai No. 281,366. i

To all whom t may concern:

Be it known that I, CHARLES F. H. BoHN- HARDT, a citizen of the UnitedStates, residing at Baltimore, and State of Maryland, have inventedcertain new and useful Improvements in Processes of and Apparatus forRenovating Coated Metal Sheets, fully described and represented in thefollowing specification and the accompanying drawings, forming a part ofthe same.

This invention relates to a process of and apparatus for renovatingcoated metal articles, and particularly sheet tin, this renovationcomprising the removal of japan, lacquer, paint or the like in orderthat the renovated sheet may be again coated.

In some arts, such, for example, as the art of making decorated bottlecaps, it isV customary to apply such coating to large.

sheets of tin, that is, tinned sheet iron or steel, the caps being.formed from these sheets. It sometimes happens that mistakes are made inthe coating and lithographic processes with the result that such sheetshave to be rejected as defective. In a plant producing such articles ona large scale the accumulation of such rejectedv sheets may beconsiderable. Attempts have been made from time to time to remove thecoating from the sheet metal in order that the rejected sheets may besaved by being recoated. So far as known, these attempts have not beensuccessful, for the reason that either the cost of removing the coatinghas been greater than the value of the defective sheet, or the tinnedsurface of the treated sheet has been so injured as to make the sheetuseless for lithographie purposes.

An object of the present invention is to,

provide a process for economically removing the coating of lacquer,japan, paint, varnish, or the like, from a sheet of metal andparticularly from so-calledsheet tin, in order that the sheet may berecoated.

A further object of the'invention is to provide an apparatus forcarrying out such a process.

With these general objects in view the invention consists in the processand the combinations, details of construction and arrangement .of partswhich will rst be described in connection with the accompanying drawingsand then more particularly pointed out.

tion, with parts broken away, of the electrolytic tank of an apparatusconstructed in Iaccordance with the invention.

Figure 2 is a sectional view taken on the line 2-2 of Fig. 3 showing(enlarged) a part of the electrotype tank.

Figure 3 is a cross-sectional view taken on the line 3 3 of Fig. 2.

Figure 4 is a transverse sectional view of the tank, the section beingtaken through a pair of rollers Figure 5 is a cross-sectional view takenon the line 5-5 of Fig. 2.

Figure 6 is a cross-sectional view taken on the line 6 of Figs. 4 and 5.

. Figure 7 is an enlarged view of a portion of the negative electrodeelement as shown in Fig. 6.

Figure 8 is a. diagrammatic viewv showing a layout of a complete plantfor carrying out the process.

In carrying out the process of the invention, the coated sheet isimmersed in an electrolytic bath which is charged with chemicals of suchcharacter as to soften the coating, the metal of the sheet beingconnected to the electric circuit so as to form one of the electrodes,preferably a cathode, for the is blistered or broken up, while theagitation of the batli removes i the' coating from the sheet. The bathcomprises an aqueous solution of such chemicals as will soften thelacquer or other coating quickly, at the same time rendering the bathproperly conductive of the electric current. With tin sheets about 24inches by 3.6 inches, having the usual coating used in decorating bottlecaps, it has been found that the process may be effectively carried outwith a 'current of about fifty amperes and about eleven and one-halfvolts. It will be found that some variation ofthe amperage and voltagemust be made to suit the varying coatings'. As the coating is usually ofnonconductive material, a thick coat of little porosity will requirehigher voltage than a thin, porous coat. As the character of the coatingdepends largely on the details of manufacture, which details are known,it is usually possible to sort the sheets so that all the sheets of agrade can be run througlh t e lthe bath with the same solution andsalts, and particularly a mixture comprising sodium sulphate, sodiumsilicate and sodium carbonate. It has been found in practice that a bathconsisting of four hundred gallons of water, thirty-tive pounds of sodaash, twenty-four pounds of silicate of soda, and fifteen pounds ofsulphate of soda, is suitable for the process described. It is advisableto thoroughly agitate the bath prior toluse in order to rapidly dissolvethe chemica s.

While the temperaturel of the bath may be varied, the best results areobtained by heating the bath considerably above the usual roomtemperatures. In practice, the bath is maintained in the neighborhood ofthe boiling int of water, generally from 200 to 212" F. With thesetemperatures the coating of lacquer or the like is rapidly softened andremoved so that the tin coating is not injured as might be the case witha long, slow treatment. This rapid treatment is particularly importantwhen the treated sheets are to be again decorated since with a slowtreatment the tin sometimes becomes roughened and does not look wellwhen lithographed.

In carrying out the process the sheets to be treated are immersed in thebath. and are at the same time included in the direct circuit in' such away that each sheet forms a cathode for the current. Meanwhile the bathis agitated, so that, as the coating. is loosened, it is carried away.This loosening or separation of the coating is probably due to the factthat, as the coating is softened by the chemical action, aided by theheat, it no longer serves to keep the electrolyte from the tin. Hence,it is likely that gas accumulates, or is formed, at the metal surface ofthe tin and loosens or blows oif the lacquer. Whether or not this is thetrue explanation, the fact remains that the coating is rapidly loosenedfrom the sheet and is washed away by the agitated liquid. Furthermore,this occurs rapidly over the entire sheet. As soon as the coating isremoved the sheet is withdrawn from the bath, washed and dried.

The accompanying drawings illustrate a form of apparatus by means ofwhich the process may be carried out on a practical scale.

Referring more particularly to Fig. 8, which illustratesdiagrammatically a complete plant, there is provided a mixlng tank 101,heated by means of a pipe 102 leading to a steam main 103 which isconnected with a suitable source. Pipe 102 is controlled by a valve 104.Water for the solution is supplied to the mixing tank by pipe 105connected with a source and controlled by valve 106. This mixing tankmay be provided with the usual form of mechanical stirring device (notshown). Connected with the mixing tank by pipe 107, which is controlledby valve 108, is an electrolytic tank 109 described more fullyhereinafter. The solution is drawn through the pipe 107 into. theelectrolytic tank after thoroughly mixing. In the embodiment hereillustrated, the mixing tank is small in comparison to the electrolytictank, thus requiring the separate mixture of several batches of solutionand in this way a more intimate mixture is insured.

To agitate the solution in the electrolytic tank, the liquid iscirculated through the tank at a relatively rapid speed and is therebydrawn into a renovating tank. To this end, a pipe 110 leads, through avalve 111, to a circulatin pump 112 of any suitable construction. gFromthe pump the solution is conducted by a pipe 113 to the top of arenovating, tank 114. This tank ,receives water from the pipe 105 and isheated from steam pipe 116. The renovating tank may be provided with ascreen for absorbing the particles of coating from the solution. pipe117, returns the solution to the electrolytic tank, this pipe beingprovided with a suitable circulating valve 118. The electrolytic tankand the renovating tank are connected with a vent pipe 119 forconducting away gases. In order that the /two tanks may be cleaned atsuitable intervals, they are respectively provided with waste pipes 1120, 120', connecting with a waste main 121.

From the electrolytic tank the treated sheets are delivered to a washtank 122 which is provided with a suitable washing means, such as aclear wa-ter spray, for washing of -the particles of coating that mayadhere to the sheets. From this Wash tank the sheets are conductedthrough two wiping or drying devices 123, 124, which may be of anysuitable construction, and lastly they pass into yan coven 125'preferably heated to about 300 F. The sheets are thus thoroughly driedand rusting is prevented.

With the exception of the electrolytic tank the abovementioned elementsare per se al1 of well-known construction and no detailed description isnecessary.

Referring more particularly to Figs. 1 to 7 the electrolyttic action iscarried on, in the present embodiment, in a watertight tank '109preferably constructed'of sheet steel and provided with a wooden coveror lid 11. The metal sheets are `fed From the renovating tank a throughthe tank by a series of insulated rollers varranged in vertical pairs.In the .which is maintained substantially constant.

.Each roller comprises a steel shaft 12 on which is mounted a pluralityof bakelized micarta roller-rings 13, and a plurality of stoneseparators 14. In the present instance, there are three roller rings andfour separators. These par-ts are clamped together on the shaft 12 bylock nuts 14 bearing against washers 16. Each shaft is journaled in abearin block 17 supported by a frame 18 prefera ly made of cast iron andresting on a wooden base 19. To rotate these rollers to feed the sheets,the upper shaft of each pair is provided, in the present embodiment,with a bevel gear 20 meshing with a pinion 21 secured to a shaft 22which extends from end to end of the tank.` This shaft 22 has, at oneend, a pulley 23 to which power is applied in any suitable manner. Inorder that both rollers of a pair may be positively driven, thereby toavoid slipping` of the sheets, the upper shaft of each pair is provided,at its opposite end, with a gear 24 meshing with a similar gear 25 onthe lower shaft. The sheets are delivered from the tank by a pair ofdelivery rollers 26 similar to those described. In order, however, thatthe sheets may be delivered at a point near the top of the tank, thesedelivery rollers 26 are carried by a bracket 27, secured to the frame 18and to the end of the tank, in an oblique position, as clearly shown inFig. 2. Owing to this position of this pair of rollers, it is the lowerone lthat .is directly driven, being provided with a bevel gear 28 whichmeshes with a pinion 29 on the main shaft 22. Between the last pair oftank rollers and the delivery rollers 26 is a guide block 30 whichdirects the sheets upwardly, and beyond the delivery rollers 26 is asecond guide block 31 which directs the sheets through an exit opening32. As appears in Fig. 1, the sheets are fed to the tank rollers bymeans of an oblique positioned pair of feed rollers 33, this feedingmechanism being a duplication of the delivery mechanism just described.

From F ig. 4 it will be seen that the rollerrings 13 are of a diameterto make contact with the metal sheets 15, whereas the separators are ofa smaller diameter to allow circulation of the solution. By means of theconstruction described, the metal sheets are fed one by one through thesolution in the electrolytic tank.

eans are provided for causing the sheets to travel in contact with oneof the electrodes, preferably the cathode. This may be accomplished, forexample, by providing a two-part cathode with resilient portions whichmake contact with opposite edges of the sheets. Altlmugh capable ofvarious constructions, in the embodiment illustrated, extending alongeach side yof the tank is an insulating bracket 40 carrying a cathodebar 41. Connected to each cathode bar is a conductor bar-42, connectedin turn to a leader 43, which is connected with a negative terminal 44.At intervals, determined by a line midway between each pair of tankrollers, each cathode bar is provided with a rounded contact member 45.These members 45 are pressed outwardly by a spring 46 so as to makecontact with the edges of the metal sheets, as appears in Fig. 6 (thesheet being represented in broken lines). In

order to complete the circuit the spring 46 is made of conductingmaterial and is in contact with both the contact members 45 and thecathode bar 41. The negative electrode (or cathode) element mayadvantageously be in electrical connection with the frame of the tank.

There is provided a second electrode arranged to be out of contact withthe sheets and at a given distance therefrom. This may comprise, forexample, a series of twopart electrode members forming a succession ofgaps through which the sheets pass, as, for example, a pair of anodes(or positive electrodes) between each two sets of rollers. Althoughcapable of various constructions, in the embodiment illustrated,extending transversely of the tank above and below the path of the metalsheets in each space between adjacent sets of tank rollers, is a pairof/supporting rods 50, 51. Carried by each.y of these rods is aplurality of porcelain insulating clamps 52, seven being shown in thepresent instance. Between each two clamps is a positive electrode memberin the form of a plate 53 extending in the direction of travel of thesheets. The upper plates 53 have their ends turned upwardly around thesupporting rods 50, and the lower plates 53 have their ends turneddownwardly around the supporting rods 51, (Fig. 2) these plates 53 beinginsulated from the rods 50, 51 by sections of porcelain tubing 54. Asappears in Fig. 3 for example, these plates 53, in the presentembodiment, form gaps through which the metal sheets are fed, the sheetsbeing out of contact with the electrode plates. Secured to the severalelectrode plates 53 of both the upper and lower series and extendingtransversely of the tank is a conducting l plate 55. The end porcelain`clamps52 are supported by bolts 56, the upper bolts 56 being suspendedfrom, and the lower ones supported on, insulating brackets 57 which arein turn secured to lugs 58 on the frame 18. Current from a positiveterminal 59 lis conducted by a leader 60 to two bus bars 61 one on eachside of the tank, which are carried by the tank lid. From one of thesebus bars, the one shown on the right in Fig` 3, a plurality of leaders62 connects the bus bar with the conducting plate 55 of the upper unitand a second serles of leaders 63 connect the other bus bar with theconducting plate 55 of the lower unit.

To serve as guides for the sheets, bolted or otherwise secured to eachof the procelain clamps 52, is a strip 65 of steel or the like,positioned lengthwise of the tank, the upper strips having their endsturned slightly upwardly, and the lower strips having their ends turneddownwardly (Fig. 2).

To heat the bath, there is provided in the bottom of the tank a set ofsteamcoils 66 connected by a pipe 67 with the main supply pipe 103.

In operation, the tank 109 being charged with the bath, previouslyprepared in mixing tank 101, the coated sheets are fed one by one to thefeed rollers 33. These rollers and the associated guide blocks deliverthe sheets to the first pair of tank rollers and the sheets are passedthrough the tank' by the successive pairs of rollers. During this travelthe opposite side edges of each sheet make contact with the springpressed members and thesheet becomes, in effect, a cathode member forthe electrolytic bath. While in contact with the members 45 the sheetsare passing between the gaps formed by the upper and lower positiveelectrode elements. 'Ehe electric circuit is traced from the positiveterminal 59, through the leader 60 to the two bus bars 61, from one busbar 61 through the several leaders 62 to the upper conducting plate 55,and thence to the upper electrode members 53; from the other bus bar 61,through the several leaders 63 to the lower plate and the lowerelectrode members 53. From the spaced positive electrode members 53 thecurrent passes through the bath to the metal plate 15, thence to thespring pressed contact members 45, throughv the springs 46 to the twoside cathode 'bars 41, the conducting bars 42v and the leader 43 to thenegative terminal 44.

During this travel of the sheets the circulating pump 112 causes a rapidcirculation of the bath in a direction opposite to the travel ofthe'sheets. As before described the coating is softened and loosened andcarried away. From the last pair of tank rollers, the sheets aredirected upwardly by guide block 30 to the delivery rollers 26 whichdeliver them through the opening 32. The sheets are then conducted tothe washing tank 122; from there to the wiping or drying devices 123,124 and finally to the oven 125 where they are thoroughly dried asdescribed.

. While the invention has been described with relation to flat sheets oftin plate it is to be understood that it is adapted to renovating otherforms of coated articles, the word sheets being used in a comprehensivesense.

lVhat is claimed is:

1. The herein described process of renovating coated tin-plated metalsheets and the hke, which comprises immersing the sheets in anelectrolytic bath charged with chemical ingredients of a character tosoften the coating, and removing the softened and loosened coating fromthe tin-plate.

2.'The herein described process of renovatin coated tin-plated metalsheets and the llke which comprises immersing zthe sheets in anelectrolytic bath charged with chemical ingredients of a character tosoften the coating, and -agitating the bath to remove the softened andloosened coating from the tin-plate.

3. The herein described process of renovatin coated tin-plated metalsheets and the llke, which comprises immersing the sheets in anelectrolytic bath charged with chemical ingredients of a character tosoften the coating,- heating the bath, and removing the softened andloosened coating from the tin-plate.

4. The herein described process of renovating coated, tin-plated metalsheets and the like, which comprises immersing the sheets in anelectrolytic hath charged with chemical ingredients of a character tosoften the coating. heating the bath to approximately the boiling pointof water. and re movinothe softened vand loosened coat-ing from thetin-plate.

5. The hereincdescribed process of renovating coated niet-al sheets andthe like, which comprises immersing the sheets inan electrolytic hathcharged with chemical ingredients of a character to soften the coating,and causing a rapid circulation of the bath to remore the softened andloosened coating. Y

6. The herein described process of renovating coated tin-plated metalsheets and the like, which consists in immersing the sheets in anclcctrolytic bath charged with chemical ingredients of a-character tosoften the coating, in contact with an electrode member, and removingthc-softened and loosened coating froni the `tin-plate.

7. The herein described process of renovating coated, tin-plated metalsheets and the like, which consists in immersing the sheets in anelectrolytic bath charged with chemical ingredients of a'character tosoften the coating, in contact with a cathode member, vand removing thesoftened and loosened coating from the tin-plate.

8. The herein described process of renovating coated, tin-plated metalsheets and the like, which consists in immersing the sheets in anelectrolytic bath, in contact with a cathode member, and removing thesoftellled and loosened coating from the tinp ate.

9. The herein described proce of renovating coated, tin-plated metalsheets and the likye which comprises immersing the sheets in anelectrolytic bath charged with an aqueous solution containing a sodiumsalt to soften the coating, and removing the scftened and loosenedcoating from the tinate.

p 10. The herein described process of renovating coated tin-plated metalsheets and the like, which comprises immersing the sheets in anelectrolytic bath charged with an aqueous solution of a mixture ofsodium salts to soften the coating, and removing the softellied andloosened coating from the tinp ate.

11. The herein described process of renovating coated metal sheetsl andthe like, which comprises immersing the sheets in an electrolytic vbathcharged with an aqueous solution of sodium sulphate, sodium silicate andsodium carbonate, and removingthe softened and loosened coating.

12. The herein described process of renovating coated, tin-plated metalsheets and the like, which comprises immersing the sheets in anelectrolytic bath charged with chemical ingredients of a character tosoften the coating, agitating the bath to remove the softened andloosened,I coating from the tin'- plate, vwashing the sheets and dryingthe sheets.

13. In apparatus for renovating coated metal sheets, and the like, andin combination a tank for containing an electrolytic bath, anode andcathode elements, and means for feeding the metal sheets through saidtank in contact with one of said electrode elements.

14. In apparatus for renovating coated metal sheets and the like, and incombination a tank for containing an electrolytic bath, anode andcathode elements, and means for feeding the metal sheets through saidtank in contact with said cathode element.

15. In apparatus for renovating coated metal sheets and the like, and incombination a tank for containing an electrolytic bath, an anodeelement, and a cathode element including a portion for contacting withthe metal sheets.

16. In apparatus for renovating coated metal sheets and the like, and incombination a tank containing an electrolytic bath, means for feedingthe metal sheets through said tank, an anode element, and a cathodeelement including spring pressed portions for contacting with the metalsheets.

17. In apparatus for renovating coated metal sheets and the like, and incombination a tank for containing an electrolytic bath, means forfeeding the metal sheets through said tank, an anode element comprisinga plurality of electrode units arranged in pairs, means for feeding themetal sheets between the members of said pairs of electric units, and acathode element having portions for contacting with the metal sheets.

18. In apparatus for renovating coated metal sheets and the like, and incombination a tank containing an electrolytic bath, an anode elementcomprising a pair of electrode members arranged to form a gap,

means for feeding the metal sheets between said electrode members andout of contact therewith, and a cathode member comprising portions forcontacting with opposite edges of the metal sheets during their travelbetween said anode members.

19. In apparatus for renovating coated metal sheets and the like, and incombination a tank for containing an electrolytic bath, an anode elementcomprising a pair of transverse plates having connection with a positiveterminal, a plurality of electrode meinbers associated with each of saidplates, means for feeding the metal sheets between said electrodemembers, and a cathode element comprising a pair of side bars havingconnection with a negative terminal and a spring pressed member havinglconnection with each side bar, for contacting with the metal sheets.

20. The herein described process of renovating metal sheets having adecorative coating, which comprises immersing the sheets in anelectrolytic bath charged with chemical ingredients of a character tosoften the decorative coating, and removing the softened and loosenedcoating.

21. In apparatus for renovating coated metal sheets and the like, and incombination a tank for containing an electrolytic bath, a plurality ofinsulated rollers arranged in pairs for feeding the sheets through saidtank, said rollers being formed to permit circulation of the bath, anelectrode element comprising spaced electrode units arranged in pairsbetween pairs'of the feeding rollers and betweeny which the sheets arefed and a complementary electrode element having a portion forcontacting with the metal sheets.

22'. In apparatus for renovating coated metal sheets and the like, andin combination, a tank for containing an electrolytic bath, a pluralityof insulated rollers arranged in pairs for feeding the sheets throughsaid tank, an electrode element withwhich the sheets are out of contact,a complementary electrode element comprising an Velectrode bar'extendingalong each side of the tank and spring-pressed contact members forcontacting with the edges of the sheets.

23. In apparatus for renovating coated metal sheets and the like, and incombination, a tank for containing an electrolytic with the other busbar, a common terminalv for said bus bars, and a complimentary electrodeelement having portions for contacting with the metal sheets.

24. In apparatus for renovating coated metal sheets and the like, and incombination, a tank for containing an electrolytic bath, means forfeeding the sheets through the tank, a plurality of connected electrodeelements arranged in pairs to form gaps through which the sheets pass, acomplementary electrode element including an electrode bar extendingalong each side of the tank, insulating Supports therefor, springpressed contact members in electrical connection with said bar.;y forcontacting with the edges of the passing sheets, conductors connectedwith said bars, leaders connected with said conductors, and a commonterminal for said leaders.

the tank, a plurality of insulated supporting rods transverse the tankand arranged in pairs straddling the path of the sheets, spacedinsulating clamps carried by said rods, electrode plates located betweensaid clamps and forming gaps through which the sheets are fed, guidestrips carried by said clamps and having their ends turned slightly awayfrom the path of the sheets, and a complementary electrode elementhaving portions for contacting with the metal sheets.

26. In apparatus for renovating coated metal sheets and the like, and incombination, a tank for containing an electrolytic bath, a plurality ofrollers arranged in pairs for feeding the sheets through the tank, thetank having in-feed and discharge openings near the top thereof, a pairof in-feed rollers obliquely arranged for feeding the sheets from thein-feed opening obliquely downwardly toward said first named rollers,and a pair of out-feed rollers obliquely arranged for feeding the sheetsfrom the first named rollers obliquely upwardly to the dischargeopening.

In testimony whereof, I have hereunto set my hand.

CHARLES F. I-I. BOHNI-IARDT.

